Baffle insert for drains

ABSTRACT

A baffle insert for conversion of conventional gravity drains into siphonic drains. The baffle insert is placed into a sump bowl of a gravity drain and by nature of its design changes hydraulic condition in the drain to a siphonic condition. The baffle insert is composed of a baffle plate and a plurality of fin extensions coupled to a bottom surface of the baffle plate. In a preferred embodiment, the number of fin extensions is 12, and the bottom surface of the baffle plate has a concave shape.

FIELD OF THE INVENTION

[0001] This invention relates to baffle inserts for roof drains.

[0002] Previously, two separate roof drain designs have been in use, a gravity drain and a siphonic drain. In the United States, gravity drains have been in a widespread use. They are characterized as weir-type design in which the rainwater flows over a rim and into a sump bowl before it enters the drainage pipe system via a spigot outlet. With this particular design, the water depth maintained on the roof is dependent on the circumference of the outer rim and to a certain extent to resistance imposed by a leaf guard. These viscous driven effects limit the rate of flow of rainwater into the drain. Therefore, the diameters of the sump bowls are relatively large in comparison to diameters of the spigot outlets to maximize the circumferential weir length and, therefore, the allowable flow rate.

[0003] A consequence of a gravity drain design is that the large rim diameter in relation to the spigot outlet diameter means that the water must flow radially inward for a certain distance along the flat sump bowl to the spigot outlet before it enters the drain piping system. Additionally, air enters the spigot outlet as well and the rainwater flows on the inner sides of the piping in a thin film. Therefore, the drain piping has to have a wide diameter in order to have a large water intake capability.

[0004] The siphonic roof drainage has been utilized since the late 1960's starting in Scandinavia and spreading throughout the world over, with the notable exception of the United States. Invented by a Finnish engineer Olavi Ebling, the concept of siphonic drainage is the achievement of full-bore flow within the drainage system through a self-priming process and then of sustaining this flow condition by eliminating the ingress of air through the roof drain. Presently, the roof drains used for siphonic drainage are designed as a whole unit with drain body, flashing hardware, and air baffle, all designed together to achieve a siphonic performance. Such drains include those designed, marketed and installed by Sommerhein, A B and others. Since siphonic drains do not take in air, the drain piping could accommodate greater volume of flowing rainwater than same diameter drain piping in a gravity drain system.

[0005] The key to the acceptance of siphonic roof drainage within the United States is the production of drain devices by North American drain manufacturers that are capable of supporting siphonic drainage systems. Requiring the use of unfamiliar drainage fixtures and pipe design techniques, siphonic drainage is currently perceived by architects, engineers and contractors as “foreign” and somewhat enigmatic technology.

[0006] What is needed is a simple and inexpensive way to convert existing drain systems to a siphonic flow capability.

SUMMARY OF THE INVENTION

[0007] The present invention achieves this goal by placing a specifically designed baffle insert into a conventional sump bowl of the gravity drain. The baffle insert has a baffle plate and a plurality of fin extensions protruding from the bottom surface of the baffle plate. The design of the baffle insert allows for creation of siphonic flow conditions inside of the drainpipe thus converting a conventional gravity drain into a siphonic drain.

BRIEF DESCRIPTION OF DRAWINGS

[0008] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings where:

[0009]FIG. 1 is a side cross-sectional view of one of the embodiments of the baffle insert.

[0010]FIG. 2 is a side cross-sectional view of one of the embodiments of the baffle insert placed inside of a sump bowl of a conventional drain.

[0011]FIG. 3 is a top view of one of the embodiment of the baffle insert.

[0012]FIG. 4 is a bottom view of one of the embodiment of the baffle insert.

[0013]FIG. 5 is a hydraulic analysis cross-sectional view partial diagram of a section of the baffle insert placed inside of a sump bowl.

DESCRIPTION OF THE INVENTION

[0014] This invention represents a baffle insert 50 depicted in FIGS. 1-4. The idea behind the disclosed baffle insert 50 design is to utilize existing conventional gravity drains used in the United States and adopt them with an air baffle/anti-vortex plate to achieve siphonic flow capability. This adaptation, however, requires hydraulic analysis in order to ensure that the baffle design is stable, will be capable of priming and minimizing the depth of water on the roof as much as possible. By properly configuring the baffle insert 50 geometry, the static pressure beneath the baffle insert 50 can be controlled thereby ensuring stable operation over a range of flows at a reasonable depth of water over the spigot outlet 12.

[0015] The baffle insert 50 is comprised of a baffle plate 1 having a central axis 2, a top surface 4, a bottom surface 5, and a lateral edge 3. A plurality of fin extensions 6 is coupled to the bottom surface 5 of the baffle plate 1 as depicted in FIGS. 1, 2 & 4. Each fin extension 6 has an outer edge 7, and a bottom edge 8, as depicted in FIGS. 1 & 2. The baffle insert 50 has an inlet entrance area 33 located under the lateral edge 3 of the baffle plate 1.

[0016] The baffle insert 50 is designed for insertion into a conventional gravity drain depicted in FIG. 2. Normally, the gravity drain has a sump bowl 11 with a rim 10 and the collected rainwater exits the sump bowl 11 by flowing through a spigot outlet 12 into a pipe 13. To convert the gravity drain into a siphonic flow drain, the baffle insert 50 is placed inside of the sump bowl 11 over the spigot outlet 12 as depicted in FIG. 2. The baffle insert 50 rests on the bottom of the sump bowl 11 with the bottom edges 8 of the fin extensions 6 being in contact with the sump bowl 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] In a preferred embodiment, the baffle insert 50 has 12 fin extensions 6 since this number was proven to be sufficient for achievement of desired results during experimental testing. The baffle plate 1 is circular in shape. The fin extensions 6 are spaced equidistantly from each other and in a radial pattern around the central axis 2, as depicted in FIG. 4. The bottom surface 5 of the baffle plate 1 has a concave shape to improve hydraulics under the baffle plate 1. Furthermore, the baffle insert 50 could have at least one anchoring extension 35 protruding from the lateral edge 3 of the baffle plate 1, where the anchoring extension 35 has means for coupling to the sump bowl 11 for prevention of spinning of the baffle insert 50 inside of the sump bowl 11. The means for coupling of the anchoring extension 35 to the sump bowl 11 are any means well known in the art such as a clamp or a simple contact with any protrusion on the inside of the sump bowl 11 as shown in FIG. 2. Alternatively any means well known in the art could be used for coupling of the baffle insert 50 with the sump bowl 11, such as welding of the bottom edges 8 of the fin extensions 6 to the bottom of the sump bowl 11. However, there is no absolute need to physically affix the baffle insert 50 to the sump bowl 11. Simple placement of the baffle insert 50 into the sump bowl 11 is enough for achievement of siphonic drain water flow.

[0018] Following is an analysis of the hydraulics involved in the design of the disclosed baffle insert 50 which should be considered with reference to a FIG. 5.

[0019] The introduction of a baffle insert 50 into the sump bowl 11 creates a restriction to the water flow path in the horizontal plane. When water flows radially inward beneath the baffle plate 1 from all sides surrounding the baffle insert 50, the available volume decreases and, therefore, the velocity must increase under the principle of continuity (i.e. Velocity×Area Constant). According to Bernoulli's principle of energy conservation, the increase in velocity also results in a reduction in static pressure.

[0020] Starting with Bernoulli's Equation: ${\frac{P_{r}}{\rho} + \frac{V_{r}^{2}}{2g} + Z_{r}} = {\frac{P_{0}}{\rho} + \frac{V_{0}^{2}}{2g} + Z_{0}}$

[0021] Where ρ is water density expressed in pounds mass (Lbm) per cubic foot. We can eliminate the P₀ term when referencing atmospheric pressure as zero (gauge). Also, the velocity at the water surface away from the inlet entrance area 33 of the baffle insert 50 is nearly zero. By eliminating these terms and rearranging to express P_(r) explicitly we have: $P_{r} = {{\rho \left( {Z_{0} - Z_{r}} \right)} - {\rho \frac{V_{r}^{2}}{2g}}}$

[0022] Because the top surface 4 of the baffle insert 50 is nearly dry or covered only by a couple of inches of water, it can be assumed that atmospheric pressure prevails on the top surface 4 of the baffle insert 50 (i.e the Zo−Zr term is insignificant). Thus, the static pressure at any point under the baffle plate 1 is less than atmospheric. The pressure profile along the radius of the sump bowl 11 during siphonic flow conditions is defined by what is called “Barlow's Curve” which is obtained by a formula derived from Bernoulli's principle while neglecting frictional flow losses under the baffle.

[0023] We can express V_(r) as follows using the principle of continuity with Ar being the flow area at the inlet entrance area 33 of the baffle insert 50: $\begin{matrix} {A_{r} = {2\quad \pi \quad {rh}}} \\ {{A_{r} \times V_{r}} = Q} \\ {V_{r} = \frac{Q}{2\quad \pi \quad {rh}}} \end{matrix}$

[0024] The term Q is the volumetric flow rate. By substituting the above expression for V_(r) into Bernoulli's equation: $P_{r} = {{\rho \left( {Z_{0} - Z_{r}} \right)} - \frac{\rho \quad Q^{2}}{8\quad \pi^{2}r^{2}h^{2}g}}$

[0025] This equation represents Pr in terms of the radial position beneath the baffle insert 50 at a given flow Q. It teaches that the static pressure beneath the baffle insert 50 decreases with the inverse square of the radius with an unbounded limit when r approaches zero.

[0026] The design of any air baffle, such as the baffle insert 50, needs to follow three main principles. It first needs to be able to prime the connected piping quickly. Thus, the height of the baffle plate 1 above the bottom of the sump bowl 11 needs to be minimized. This will help achieve a high Reynolds Number beneath the baffle plate 1 and the necessary turbulence for proper air to water mixing. Second, the baffle insert 50 must not introduce a limiting effect with respect to maximum flow. In other words, it is advantageous for the drain to be limited in maximum flow capacity by the fixed spigot outlet 12 diameter and not by the introduction of a baffle insert 50. Finally, the first two goals must be balanced with the desire to have a minimum of water depth on the roof above the baffle insert 50, which means that the resistance of the baffle insert 50/drain combination should be minimized.

[0027] The static pressure (in this case, negative pressure) under the baffle insert 50 is an important parameter for any baffle design because there is a limit to negative pressure under the baffle. If the static pressure beneath the baffle reaches water's vapor pressure at the ambient temperature, spontaneous flashing of water into vapor will occur resulting in a phenomenon known as “cavitation.” This condition is characterized by alarming noise, vibrations and a disruption in flow. Thus, there is an upper limit to flow capability through the drain in siphonic action.

[0028] The flat sump bowl 11 design of conventional roof drains precludes the efficiency of a flat plate or convex baffle as this geometry compounds the drop in static pressure as water flows radially toward the spigot outlet 12. Our approach to the baffle insert 50 design was to limit the maximum velocity beneath the baffle insert 50 to minimize the Barlow Curve effects. It is possible to maintain a stable static pressure beneath the baffle plate 1. Since the direction of flow is horizontal, potential energy effects do not come into play. If the effects of friction losses are ignored, the development of the static pressure along the radial dimension is controlled only by the velocity head term in Bernoulli's energy equation. In order to maintain and control a maximum static pressure drop, the velocity must be limited to some maximum value in the direction of flow.

[0029] This requirement is possible to achieve if the baffle plate 1 is given an upward slope on the bottom surface 5 from the lateral edge 3 towards the central axis 2. This concave geometry, shown in FIGS. 1, 2 & 5, is intended to maintain a limit to the water velocity beneath the baffle plate 1.

[0030] The first step in determining the dimensions of the baffle insert 50 is to set the minimum height of H_(i) at the inlet entrance area 33 where the water enters the drain. The first principle design feature is to allow the system to prime quickly, but there is a minimum height above the sump bowl 11 that will assure the achievement of the second principle, to ensure that the maximum velocity below the baffle plate 1 does not exceed the velocity within the spigot outlet 12. Since the drain manufacturer fixes the radius of the spigot outlet 12, the velocity at the spigot outlet 12 V_(o), sets the maximum velocity at the inlet entrance area 33. We want V_(i) to be less than or equal to V_(o). We can express the velocity in the spigot outlet 12 in terms of the water flow rate as follows: $V_{0} = \frac{Q}{\quad {\pi \quad R_{0}^{2}}}$

[0031] Where Q is the volumetric flow rate and Ro is the spigot outlet 12 radius.

[0032] The water velocity at the inlet entrance area 33 can also be expressed in terms of the flow and the inlet entrance area 33 geometry. The analysis of the cross-sectional area below the baffle plate 1 needs to account for the presence of the fin extensions 6. These fin extensions 6 are an integral part of the baffle insert 50 design. They serve three main purposes:

[0033] 1. They prevent or diminish the rotation of the inflowing water (i.e. vortices).

[0034] 2. They assist in the mixing of water and air during the initial phase of priming thus minimizing the priming time for the device and the connected piping.

[0035] 3. The fin extensions 6 transfer the force created by the differential pressures across the baffle insert 50 to the bottom of the sump bowl 11.

[0036] The number of fin extensions 6 is optional, however, in order to minimize rotation and maximize air mixing, 12 fin extensions 6 have been chosen for this design. The fin extensions 6 occupy a certain area that has to be considered when calculating velocities beneath the baffle plate 1.

[0037] At the inlet entrance area 33 of the baffle insert 50, we apply the same principle of continuity to express the inlet velocity (Vi) in terms of the flow rate as follows:

A _(i)=2πR _(d) H _(i) −ntH _(i)

[0038] In this expression, the area at the inlet entrance area 33 is the circumference of the baffle plate 1 (if the baffle plate 1 is round) times the height less the area taken up by the fin extensions 6 where n is the number of fin extensions 6 and t is their thickness.

[0039] Thus: $V_{i} = \frac{Q}{{2\quad \pi \quad R_{d}H_{i}} - {n\quad t\quad H_{i}}}$

[0040] By setting Vi=Vo, we see that the flow rate drops from the analysis and only the two areas are left (i.e. the cross-sectional flow areas at each station must be equal). After some rearranging: $H_{i} = \frac{\quad {\pi \quad R_{0}^{2}}}{{2\quad \pi \quad R_{d}} - {n\quad t}}$

[0041] For the 4″ outlet drain (102 mm), the spigot outlet 12 radius (Ro) is 2.0 inches (51 mm), the baffle plate 1 radius is set at 4.33 inches (110 mm), the number of fin extensions 6 chosen is 12 and the fin extensions' 6 thickness is 0.25 inches. Substituting these numbers into the above equation, the minimum height at the inlet entrance area 33 (Hi) is 0.52 inches. In our design, we set the height well above that minimum height to 1.1 inches (28 mm) to ensure a stable design. The primary reason for this is to assist in limiting the resistance value of the baffle insert 50 while still maintaining a reasonably minimum clearance to assist in quick priming.

[0042] The goal of the design at this stage is to then set the radial velocity Vr to a maximum allowable value beneath the baffle plate 1. This is achieved by pitching the bottom surface 5 of the baffle plate 1 upward and away from the flat bottom of the sump bowl 11. The desired result of this pitch is to allow a velocity head no greater than that achieved in the fixed spigot outlet 12. Thus, the maximum flow capacity of the drain is limited only by the spigot outlet 12 dimension and not the baffle insert 50. The flow cross-sectional area can be expressed for any value of r between Rd and Ro as follows:

A _(r)=(2πr−nt)(H _(i)+(R _(d) −r)tan α)

[0043] Alpha is the slope of the bottom side 5 of the baffle plate 1. In this case the height of the inlet entrance area 33 is no longer a constant value as it would be if the baffle plate 1 was a flat disc—the height increases as r decreases. Again setting the spigot outlet 12 area equal to the flow cross-sectional area below the baffle plate 1, we get: $\alpha = {\arctan \left\lbrack {\frac{\quad {\pi \quad R_{0}^{2}}}{\left( {R_{d} - r} \right)\left( {{2\quad \pi \quad r} - {n\quad t}} \right)} - \frac{H_{i}}{\left( {R_{d} - r} \right)}} \right\rbrack}$

[0044] The point just before the spigot outlet 12 would have the highest velocity if the baffle plate 1 were not pitched. Thus, solving for alpha at r=Ro will give the minimum pitch required. With Ro=2, Rd=4.33, Hi=1.1, n=12, and t=0.25 we find the value of alpha to be a minimum of 5.2 degrees.

[0045] With this resulting pitch, we go back to compute the velocity head in the spigot outlet 12 at a unit flow of 1 cubic foot per second. With the inner diameter being 4″, the resulting velocity head is 2.04 ft. The velocity head of the water just before it reaches the edge of the spigot outlet 12 is computed to be also 2.04 ft. The velocity head at the inlet entrance area 33 of the baffle is 0.45 ft. Thus, the designed geometry allows the converted drain to operate at its highest possible capacity while maintaining a safe design without cavitation effects.

[0046] The tested prototype has an inner slope on the bottom surface 5 of the baffle plate 1 of 5.0 degrees for simplicity of construction. During flow tests, the baffle insert 50 performed according to theory and should constitute a safe and stable design when put into production. 

What is claimed is:
 1. A baffle insert for drains, comprising: a baffle plate, having a central axis, a lateral edge, a top surface, and a bottom surface; a plurality of fin extensions coupled to the bottom surface of the baffle plate.
 2. The baffle insert of claim 1 wherein: each fin extension has an outer edge, and a bottom edge.
 3. The baffle insert of claim 1 wherein: the fin extensions are arranged in a radial pattern with respect to the central axis of the baffle plate.
 4. The baffle insert of claim 1 further comprising: an inlet entrance area located under the lateral edge of the baffle plate.
 5. The baffle insert of claim 1 wherein: the bottom surface of the baffle plate is slopped upwards from the lateral edge towards the central axis.
 6. The baffle insert of claim 1 wherein: the bottom surface of the baffle plate has a concave shape.
 7. The baffle insert of claim 1 wherein: the lateral edge of the baffle plate has at least one anchoring extension.
 8. The baffle insert of claim 1 further comprising: means for coupling of the baffle insert to a sump bowl of a drain.
 9. The baffle insert of claim 1 wherein: the fin extensions are spaced equidistantly from each other.
 10. The baffle insert of claim 1 wherein: each fin extension has a substantially vertical orientation.
 11. The baffle insert of claim 1 wherein: the baffle insert is integrated with a sump bowl of a drain.
 12. The baffle insert of claim 1 wherein: the baffle plate has a round shape.
 13. A baffle insert for drains, comprising: a round baffle plate, having a central axis, a lateral edge, a top surface, and a bottom surface; a plurality of fin extensions coupled to the bottom surface of the baffle plate, wherein the fin extensions are arranged in a radial pattern with respect to the central axis of the baffle plate, and wherein each fin extension has an outer edge, and a bottom edge.
 14. The baffle insert of claim 13 further comprising: an inlet entrance area located under the lateral edge of the baffle plate.
 15. The baffle insert of claim 13 wherein: the bottom surface of the baffle plate is slopped upwards from the lateral edge towards the central axis.
 16. The baffle insert of claim 13 wherein: the bottom surface of the baffle plate has a concave shape.
 17. The baffle insert of claim 13 wherein: the lateral edge of the baffle plate has at least one anchoring extension.
 18. The baffle insert of claim 13 further comprising: means for coupling of the baffle insert to a sump bowl of a drain.
 19. The baffle insert of claim 13 wherein: the fin extensions are spaced equidistantly from each other and each fin extension has a substantially vertical orientation.
 20. The baffle insert of claim 13 wherein: the baffle insert is integrated with a sump bowl of a drain. 